2 results
Search Results
Now showing 1 - 2 of 2
- ItemSimultaneous lidar observations of a polar stratospheric cloud on the east and west sides of the Scandinavian mountains and microphysical box model simulations(München : European Geopyhsical Union, 2006) Blum, U.; Khosrawi, F.; Baumgarten, G.; Stebel, K.; Müller, R.; Fricke, K.H.The importance of polar stratospheric clouds (PSC) for polar ozone depletion is well established. Lidar experiments are well suited to observe and classify polar stratospheric clouds. On 5 January 2005 a PSC was observed simultaneously on the east and west sides of the Scandinavian mountains by ground-based lidars. This cloud was composed of liquid particles with a mixture of solid particles in the upper part of the cloud. Multi-colour measurements revealed that the liquid particles had a mode radius of r≈300 nm, a distribution width of σ≈1.04 and an altitude dependent number density of N≈2–20 cm−3. Simulations with a microphysical box model show that the cloud had formed about 20 h before observation. High HNO3 concentrations in the PSC of 40–50 weight percent were simulated in the altitude regions where the liquid particles were observed, while this concentration was reduced to about 10 weight percent in that part of the cloud where a mixture between solid and liquid particles was observed by the lidar. The model simulations also revealed a very narrow particle size distribution with values similar to the lidar observations. Below and above the cloud almost no HNO3 uptake was simulated. Although the PSC shows distinct wave signatures, no gravity wave activity was observed in the temperature profiles measured by the lidars and meteorological analyses support this observation. The observed cloud must have formed in a wave field above Iceland about 20 h prior to the measurements and the cloud wave pattern was advected by the background wind to Scandinavia. In this wave field above Iceland temperatures potentially dropped below the ice formation temperature, so that ice clouds may have formed which can act as condensation nuclei for the nitric acid trihydrate (NAT) particles observed at the cloud top above Esrange.
- ItemA method for detecting the presence of organic fraction in nucleation mode sized particles(München : European Geopyhsical Union, 2005) Vaattovaara, P.; Räsänen, M.; Kühn, T.; Joutsensaari, J.; Laaksonen, A.New particle formation and growth has a very important role in many climate processes. However, the overall knowlegde of the chemical composition of atmospheric nucleation mode (particle diameter, d<20 nm) and the lower end of Aitken mode particles (d≤50 nm) is still insufficient. In this work, we have applied the UFO-TDMA (ultrafine organic tandem differential mobility analyzer) method to shed light on the presence of an organic fraction in the nucleation mode size class in different atmospheric environments. The basic principle of the organic fraction detection is based on our laboratory UFO-TDMA measurements with organic and inorganic compounds. Our laboratory measurements indicate that the usefulness of the UFO-TDMA in the field experiments would arise especially from the fact that atmospherically the most relevant inorganic compounds do not grow in subsaturated ethanol vapor, when particle size is 10 nm in diameter and saturation ratio is about 86% or below it. Furthermore, internally mixed particles composed of ammonium bisulfate and sulfuric acid with sulfuric acid mass fraction ≤33% show no growth at 85% saturation ratio. In contrast, 10 nm particles composed of various oxidized organic compounds of atmospheric relevance are able to grow in those conditions. These discoveries indicate that it is possible to detect the presence of organics in atmospheric nucleation mode sized particles using the UFO-TDMA method. In the future, the UFO-TDMA is expected to be an important aid to describe the composition of atmospheric newly-formed particles.